This invention relates to processes for stabilizing aqueous solutions of alkali metal aluminates and zirconates.
Alkali metal aluminates and zirconates, particularly sodium and potassium aluminates and zirconates, have a wide variety of commercial uses. They are employed in large amounts, e.g., in the manufacture of paper, in the purification of water, in the manufacture of catalysts and in the surface treatment of titanium dioxide. For many of these uses aqueous solutions of the aluminates and zirconates are preferred, and consequently large quantities of these solutions are used in commerce. A disadvantage of these aqueous solutions has been that they are not stable to long term storage at ambient temperatures. This is evidenced by the precipitation of solids, which cannot readily be put back into solution. This instability is generally made worse by the presence of iron and other heavy metal contaminants.
Organic compounds such as gluconic acid and tartaric acid have been used to stabilize aluminate and zirconate solutions, and U.S. Pat. No. 3,656,889, which is incorporated by reference herein in its entirety, discloses the use of a synergistic blend of tartaric and gluconic acids to stabilize sodium aluminate solutions. However, there are applications, e.g., acceleration of the setting of concrete with potassium aluminate, catalyst manufacture and surface treatment of titanium dioxide, where the presence of tataric and gluconic acids is undesirable.
For this reason, there is a need in the industry for a method of stabilizing alkali metal aluminate and zirconate solutions without the use of organic stabilizing agents such as gluconates or tartrates.
This invention relates to a process of stabilizing an aqueous solution of alkali metal aluminate or zirconate comprising adding to the solution an alkali metal carbonate in an amount sufficient to prevent precipitation of solids from the solution for at least about 3 months at 15-25xc2x0 C. In another embodiment the invention relates to a process of stabilizing an aqueous alkali metal aluminate solution comprising adding to the solution an alkali metal carbonate in an amount sufficient to prevent precipitation of solids from the solution for at least about 3 months, wherein the solution contains no alkali metal salts of organic acids having greater than 1 carbon atom.